1. Field of the Invention
The present invention relates to an outside air determination apparatus disposed in a vehicle for determining an outside air temperature.
2. Description of the Related Art
Conventionally, there has been known an outside air temperature determination apparatus including an outside air temperature detection means disposed in an automobile for detecting an outside air temperature and a control means for setting the detection temperature detected by the outside air temperature detection means as a determination value. The determination value obtained by the outside air temperature determination apparatus is output to, for example, a display device disposed inside the automobile to be displayed as an outside air temperature (for example, refer to Japanese Patent Laid-open No. H1-212637).
The outside air temperature determination apparatus disclosed in Japanese Patent Laid-open No. H1-212637 includes a speed detection means for detecting a vehicular speed of the automobile and a memory for storing the determination value. When a vehicular speed detected by the speed detection means is not lower than 20 km/h, the control means compares the detection temperature detected by the outside air temperature detection means with the determination value stored in memory, and if the detection temperature is higher than the determination value, the control means performs a process by adding 1□ to the determination value and storing the result in memory; on the other hand, if the detection temperature is lower than the determination value, the control means performs a process by subtracting 1° C. from the determination value and storing the result in memory.
When a vehicular speed detected by the speed detection means is lower than 20 km/h, the control means performs an increment prohibition processing to prohibit an increment from being added to the determination value even though the detection temperature is higher than the determination value. Accordingly, a wrong temperature may be prevented from being displayed on a display device since the detection temperature detected by the outside air temperature detection means may become higher than real outside air temperature due to radiation heat from a radiator or the like when the automobile travels at a low speed caused by a traffic jam or the like.
The outside air temperature detection means of the conventional outside air temperature determination apparatus is mounted on a front portion of the automobile and detects an air temperature of air inhaled from a radiator grill for cooling the radiator. The outside air temperature detection means is provided with a protection cover to prevent the characteristics of the outside air temperature detection means from being deteriorated by a flying stone, thermal strain according to the radiation heat from such as the radiator, or the like, thus it costs some time for heat of the outside air temperature to be transferred to the outside air temperature detection means.
For the outside air temperature determination apparatus with the above-mentioned configuration, even in cases where the vehicular speed detected by the speed detection means is accelerated equal to or greater than 20 km/h from a speed below 20 km/h, and as a result thereof, the radiation heat from such as the radiator or the like exerts no effect on the detection temperature detected by the outside air temperature detection means, it costs some time for the outside air temperature detection means to sufficiently radiate heat so as to get ready for detecting real outside air temperature appropriately.
Therefore in the conventional outside air temperature determination apparatus, when the vehicular speed detected by the speed detection means is accelerated equal to or greater than 20 km/h from a speed below 20 km/h, even though real outside air temperature is lower than the determination value stored in memory, the processing of adding an increment to the determination value is performed during a duration in which the detection temperature detected by the outside air temperature detection means maintains at a higher temperature for a long time due to the affect from the radiation heat from such as the radiator or the like. Resultantly, there arises a problem that a great deviation appears between real outside air temperature and the determination value. The detection temperature detected by the outside air temperature detection means approximates to real outside air temperature as the time lapses, and eventually the determination value also approximates to real outside air temperature, thereby enabling the outside air temperature to be determined appropriately. However, it will take too much time to reach the aforementioned state.